To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. The wide-spreading flash memory market and the demand for increased storage capacities drive forward the miniaturization technology. As the advanced miniaturization technology, manufacturing of microelectronic devices at the 65-nm node by the ArF lithography has been implemented in a mass scale. Manufacturing of 45-nm node devices by the next generation ArF immersion lithography is approaching to the verge of high-volume application. The candidates for the future generation 32-nm node include ultra-high NA lens immersion lithography using a liquid having a higher refractive index than water in combination with a high refractive index lens and a high refractive index resist film, EUV lithography of 13.5 nm wavelength, and double patterning version of the ArF lithography, on which active research efforts have been made.
With respect to high-energy radiation of very short wavelength such as EB or x-ray, hydrocarbons and similar light elements used in resist materials have little absorption. Then polyhydroxystyrene base resist materials are under consideration.
Resist materials for EB lithography are practically used in the mask image writing application. Recently, the mask manufacturing technology becomes of greater interest. Reduction projection exposure systems or steppers have been used since the time when the exposure light was g-line. While their demagnification factor was ⅕, a factor of ¼ is now used as a result of chip size enlargement and projection lens diameter increase. It becomes of concern that a dimensional error of a mask has an impact on the dimensional variation of a pattern on wafer. It is pointed out that as the pattern feature is reduced, the value of a dimensional variation on the wafer becomes greater than the value of a dimensional error of the mask. This is evaluated by a mask error enhancement factor (MEEF) which is a dimensional variation on wafer divided by a dimensional error of mask. Patterns on the order of 45 nm often show an MEEF in excess of 4. In a situation including a demagnification factor of ¼ and a MEEF of 4, the mask manufacture needs an accuracy substantially equivalent to that for equi-magnification masks.
The exposure system for mask manufacturing made a transition from the laser beam exposure system to the EB exposure system to increase the accuracy of line width. Since a further size reduction becomes possible by increasing the accelerating voltage of the electron gun in the EB exposure system, the accelerating voltage has increased from 10 keV to 30 keV and reached 50 keV in the current mainstream system, with a voltage of 100 keV being under investigation.
Chemically amplified resist compositions comprising an acid generator capable of generating an acid upon exposure to light or EB include chemically amplified positive resist compositions wherein deprotection reaction takes place under the action of acid and chemically amplified negative resist compositions wherein crosslinking reaction takes place under the action of acid. Quenchers are often added to these resist compositions for the purpose of controlling the diffusion of the acid to unexposed areas to improve the contrast. The addition of quenchers is fully effective to this purpose. A number of amine quenchers were proposed as disclosed in Patent Documents 1 to 3.
As the pattern feature size is reduced, approaching to the diffraction limit of light, light contrast lowers. In the case of positive resist film, a lowering of light contrast leads to reductions of resolution and focus margin of hole and trench patterns.
For mitigating the influence of reduced resolution of resist pattern due to a lowering of light contrast, an attempt is made to enhance the dissolution contrast of resist film. One such attempt is a chemically amplified resist material utilizing an acid amplifying mechanism that a compound is decomposed with an acid to generate another acid. In general, the concentration of acid creeps up linearly with an increase of exposure dose. In the case of the acid amplifying mechanism, the concentration of acid jumps up non-linearly as the exposure dose increases. The acid amplifying system is beneficial for further enhancing the advantages of chemically amplified resist film including high contrast and high sensitivity, but worsens the drawbacks of chemically amplified resist film that environmental resistance is degraded by amine contamination and maximum resolution is reduced by an increase of acid diffusion distance. The acid amplifying system is very difficult to control when implemented in practice.
Another approach for enhanced contrast is by reducing the concentration of amine with an increasing exposure dose. This may be achieved by applying a compound which loses the function of quencher upon light exposure.
With respect to the acid labile group used in methacrylate polymers for the ArF lithography, deprotection reaction takes place when a photoacid generator capable of generating a sulfonic acid having fluorine substituted at α-position (referred to “α-fluorinated sulfonic acid”) is used, but not when an acid generator capable of generating a sulfonic acid not having fluorine substituted at α-position (referred to “α-non-fluorinated sulfonic acid”) or carboxylic acid is used. If a sulfonium or iodonium salt capable of generating an α-fluorinated sulfonic acid is combined with a sulfonium or iodonium salt capable of generating an α-non-fluorinated sulfonic acid, the sulfonium or iodonium salt capable of generating an α-non-fluorinated sulfonic acid undergoes ion exchange with the α-fluorinated sulfonic acid. Through the ion exchange, the α-fluorinated sulfonic acid thus generated by light exposure is converted back to the sulfonium or iodonium salt while the sulfonium or iodonium salt of an α-non-fluorinated sulfonic acid or carboxylic acid functions as a quencher.
Further, the sulfonium or iodonium salt capable of generating an α-non-fluorinated sulfonic acid also functions as a photodegradable quencher since it loses the quencher function by photodegradation.
Non-Patent Document 3 points out that the addition of a photodegradable quencher expands the margin of a trench pattern although the structural formula is not illustrated. However, it has only a little influence on performance improvement. There is a desire to have a quencher for further improving contrast.
Patent Document 4 discloses an amine quencher which reduces its basicity through a mechanism that an acid labile group is eliminated under the action of acid, and lactam is then formed. Due to the mechanism that basicity is reduced under the action of acid, acid diffusion is controlled by high basicity in the unexposed region where the amount of acid generated is minimal, whereas acid diffusion is promoted due to reduced basicity of the quencher in the overexposed region where the amount of acid generated is large. This expands the difference in acid amount between the exposed and unexposed regions, from which an improvement in contrast is expected. However, the contrast enhancing effect is low since deprotection reaction of the base polymer and deprotection reaction of the quencher and ensuing lactam-forming reaction take place simultaneously in parallel. If the deprotection reaction of the quencher is slower than the deprotection reaction of the base polymer, the contrast enhancing effect is lower. There is a desire to have a quencher capable of further contrast improvement.